1. Field of the Invention
The present invention relates to a method of mounting a semiconductor device to a substrate and a mounted structure thereof and, more in particular, to a method of mounting a semiconductor device to a substrate by a flip-chip system and a mounting structure thereof.
2. Description of the Related Art
Accompanying with reduction in the size and lowering of the cost in electronic equipments in recent years, a structure for mounting semiconductor devices on a substrate at a high density has been simplified. A flip-chip system has been proposed as a high density mounting structure of semiconductor devices having such a simplified structure.
In the flip-chip system, a semiconductor device with a plurality of bump electrodes being mounted to at least one surface thereof is connected to a circuit substrate with the surface being faced downward, which is disclosed in Japanese Patent Laid-Open Hei 4-82241. Now, the conventional flip-chip mounting structure will be described with reference to FIG. 1.
Referring to FIG. 1, an insulating resin layer 2 made of a material such as rubber having elastic recovery force is formed on a substrate 1. Further, a mounting pad 3 is formed on the insulating resin layer 2 by means of sputtering or vapor deposition. An sealing resin 5 is coated to a region on the insulating resin layer 2 in which a semiconductor device 4 is mounted to the substrate 1. On the other hand, a plurality of bump electrodes 6 are formed to the surface of the semiconductor device 4 facing the substrate 1.
In the manufacturing method of the conventional mounting structure, at first, a plurality of the bump electrodes 6 disposed on the lower surface of the semiconductor device 4 and the mounting pad on the substrate 1 are aligned and then the semiconductor device 4 is bonded under pressure on the substrate 1. In this case, since the sealing resin 5 between the bump electrode 6 of the semiconductor device 4 and the mounting pad 3 on the substrate 1 is extruded, the bump electrode 6 and the mounted pad 3 are connected electrically with each other. In this conventional flip-chip mounting structure, since the insulating resin layer 2 having the elastic recovery force is formed between the substrate 1 and the mounting pad 3, electric connection between the bump electrode 6 and the mounting pad 3 can be held stably by the elastic recovery force of the insulating resin layer 2 and the contracting force of the sealing resin 5.
However, in the conventional flip-chip mounting structure, the elastic recovery force of the insulating resin layer 2 or the contracting force of the sealing resin 5 tends to suffer from degradation in an accelerated test such as a temperature cycle test and, as a result, the amount of heat expansion of the sealing resin 5 is greater than the contracting force thereof and the elastic recovery force of the insulating resin layer 2, to form a gap between the bump electrode 6 and the mounting pad 3. Accordingly, the gap formed between the bump electrode 6 and the mounting pad 3 causes connection failure between the semiconductor device 4 and the substrate 1.
Further, in the conventional flip-chip mounting structure described above, the semiconductor device 4 and the substrate 1 are connected in a state where the mounting pad 3 and the insulating resin layer 2 are deformed elastically. Accordingly, when the balance between the contracting force of the sealing resin 5 and the elastic recovery force of the insulating resin layer 2 should change by the temperature change, the deformed state of the mounting pad 3 changes correspondingly. Thus, considerable stresses exert on the mounting pad 3 due to temperature change and, as a result, the mounting pad 3 is damaged to sometimes cause disconnection or the like.
Further, in the conventional flip-chip structure, since it is necessary to form the insulating resin layer 2 having the elastic recovery force on the substrate 1, it cannot avoid the complexity for the production step and increase of the production cost.